As the San Francisco Board of Supervisors prepares to place a 2-cents-per-ounce soda tax on the November ballot at its Tuesday meeting, the city's economist has released a report predicting the tax would lead San Franciscans to reduce their soda consumption by 31 percent.

City economist Ted Egan said city residents drink a total of about 3 billion ounces of sugary drinks every year, and that the tax would likely raise the price of sodas by 23 to 36 percent. The price hike would encourage people to buy less soda, thereby lowering the rate of obesity and chronic disease, and reducing public and private health costs in the city, he said.

The report is being cited by proponents of the soda tax, who will have a costly fight on their hands to persuade the required two-thirds of city voters to support the measure and make San Francisco the first city in the nation to levy a surcharge on sodas and other sweetened beverages.

Battle with beverage lobby

The deep-pocketed American Beverage Association has successfully beaten back similar attempts in cities and towns around the country, and supporters of the soda tax expect it to spend more than $10 million to defeat the San Francisco measure and a similar measure on the November ballot in Berkeley. If spending does hit that mark, the campaign would be the costliest of any ballot measure fight in San Francisco history.

"We're well aware of the tidal wave of money that's going to hit our city from the American Beverage Association," said Supervisor Scott Wiener, one of the authors of the soda tax measure. "Given San Francisco's long history of being on the cutting edge of public health issues and given the kind of campaign we've been running, we think we have a reasonable shot at winning."

Roger Salazar, a spokesman for the campaign to defeat the soda tax, said the beverage association has not committed any particular dollar amount to the campaign. He said what he found most interesting in Egan's report was the finding that the tax would hit low-income communities hardest because they drink the most soda.

"This is a burden that is going to be placed on people who can least afford it," Salazar said. "We think at the end of the day voters in San Francisco and Berkeley are going to see that this is not the way to prioritize the city's activities."

Mayor remains neutral

Eight of the 11 San Francisco supervisors are on the record as backing the tax, and proponents hope Tuesday's vote placing it on the ballot will be unanimous. Supporters of the soda tax also include the school board, a number of local parent-teacher associations, the teachers union, several medical groups and local food banks.

Notably absent from the lengthy list of early endorsers of the measure is Mayor Ed Lee, who has taken no position. His spokesman, Francis Tsang, said the mayor supports the idea in theory but is concerned that it will prove a distraction on November's lengthy ballot. Lee's top priorities are measures related to housing and transportation, Tsang said.

Unlike Berkeley's proposed 1-cent-per-ounce tax, which would go into the city's general fund, San Francisco's 2-cents-per-ounce tax would go to nutrition and physical education programs. San Francisco supporters had previously estimated the tax would raise $31 million a year, but Egan's report says it would actually bring in $35 million to $54 million annually.

The San Francisco tax would apply to drinks that have added sugar and contain more than 25 calories per 12 ounces. Diet sodas, alcoholic drinks, infant formula, milk and nondairy creamers would not be taxed, but concentrates used to make juice and other drinks would be. The tax would be levied on the first distributor of the products within city limits - usually a grocery store or other retail outlet, though the surcharge is expected to be passed on to consumers.

Where the money goes

Two percent of the money raised from the tax will be used for administrative costs.

Of the rest, 40 percent will go to the school district to use for student nutrition, gardening, cooking classes, after-school programs and physical education.

Twenty-five percent will be split by the Department of Public Health and the Public Utilities Commission to promote healthful food and drinks, and build more drinking fountains and water bottle refilling stations.

An additional 25 percent will go to the Recreation and Park Department for athletic programs and recreation centers, and 10 percent will go to community groups that support nutrition and recreation.

On the cutting edge of health

The soda tax ballot measure is just the most recent example of San Francisco officials pushing innovative policies intended to make residents healthier, but it has been slammed by opponents as creating a nanny state. Here are some earlier examples.

1993: San Francisco was at the forefront of smoking bans when the Board of Supervisors voted to prohibit lighting up in workplaces, restaurants and public arenas. Numerous other restrictions on smoking have followed, including a 2005 law banning smoking in city parks and playing fields.

2008: San Francisco became the first city in the country to ban the sale of cigarettes in drugstores.

2008: The supervisors followed New York City's lead and voted to mandate that calorie counts be included on chain restaurant menus.

2010: The Board of Supervisors voted to ban free toys in Happy Meals and other unhealthful fast-food meals aimed at kids.